1. Field of the Invention
The invention pertains to a multifunction probe for aircraft, intended for determining aerodynamic parameters of an airflow surrounding the aircraft.
2. Discussion of the Background
The piloting of any aircraft involves knowing the relative speed of the aircraft with respect to the airflow surrounding it, that is to say to the relative wind. This speed is determined with the aid of sensors of the static pressure Ps, of the total pressure Pt and of the angle of incidence xcex1. xcex1 provides the direction of the speed vector in a reference system tied to the aircraft and Pt-Ps provides the modulus of this vector. The three aerodynamic parameters therefore make it possible to determine the speed vector of an airplane and, as the case may be, of a so-called convertible tilt-rotor aircraft.
The invention pertains more especially to a probe comprising a movable blade intended to orient itself along the axis of the flow. In a known manner, the movable blade comprises several pressure taps suitable for the measurement of each parameter. The blade comprises in particular a first total pressure Pt tap in the form of an orifice opening out perpendicularly to the flow. This orifice can be placed at the end of a tube whose axis is substantially parallel to the flow. This tube is better known as a Pitot tube.
The blade also comprises a second static pressure Ps tap. Customarily, this second tap comprises two orifices each located on one of the faces of the blade. These two orifices are in communication with a chamber located inside the blade. The chamber makes it possible to average the pressure between the two orifices of the second pressure tap.
The blade also comprises a third pressure tap making it possible to determine the angle of incidence xcex1 of the blade with respect to the ambient airflow. This third pressure tap comprises, like the static pressure tap, two orifices, each located on one of the faces of the blade. However, unlike in the case of the static pressure Ps tap, the two orifices of the angle of incidence xcex1 pressure tap do not communicate with one another and the pressure difference between the two orifices makes it possible to determine the angle of incidence xcex1 of the blade. In order to improve the sensitivity of the measurement of angle of incidence xcex1, these two orifices are located in the vicinity of the leading edge of the blade.
The blade described above comprises a pressure tap for each parameter to be measured. Each pressure tap comprises one or more orifices linked by channels to pressure sensors which are usually located in the base of the probe. This base being fixed, it is necessary to provide a rotating pneumatic manifold so as to link each orifice located in the moving blade to the pressure sensor associated therewith in the fixed part of the probe.
The aim of the invention is to simplify the probe by reducing the number of pressure taps, the number of channels and consequently the construction of the rotating pneumatic manifold while ensuring the determination of the three aerodynamic parameters Pt, Ps and xcex1.
To achieve this aim, the subject of the invention is a multifunction probe for aircraft intended for determining in particular the static pressure and the total pressure of an airflow located in the vicinity of the aircraft and the angle of incidence of the aircraft with respect to the flow, the probe comprising a movable blade intended to orient itself along the axis of the airflow, the movable blade comprising at least one static pressure tap orifice located on one side of the blade and a pressure tap intended for measuring the angle of incidence of the blade with respect to the flow, characterized in that the probe furthermore comprises pressure measurement means associated with each pressure tap and means for calculating the total pressure of the flow as a function of the measurements carried out by the various measurement means of the probe.
By dispensing with any total pressure tap in the blade in accordance with the invention it is possible to simplify other constituents of the probe such as in particular the deicing circuit required to avoid the formation of ice on the blade when the aircraft is flying at high altitude and is subjected to temperatures markedly below zero degrees Celsius. The ice may modify the aerodynamic shape of the blade and obstruct the orifices of the pressure taps, thereby causing erroneous measurements of the aerodynamic parameters. The deicing circuit is commonly made in the form of an electric resistor heating the body of the blade. A Pitot tube used as a total pressure Pt tap is relatively voluminous as compared with the blade as a whole and the deicing circuit associated therewith consumes of the order of a third of the electric power required for deicing the blade as a whole. It is readily seen that by dispensing with the Pitot tube it is possible to simplify the deicing circuit.
The invention also finds its benefit when the Pitot tube or more generally the total pressure Pt tap is made some distance from a blade comprising just a static pressure Ps tap and an angle of incidence xcex1 pressure tap. The invention consequently makes it possible to do away with the Pitot tube and the corresponding opening in the skin of the aircraft.